Information recording media and information recording drive

ABSTRACT

A magneto-optical storage apparatus including an ultra-high density information recording media having an inorganic compound layer  12  on a substrate  11,  and in the inorganic compound layer  12,  an oxide of at least one kind selected from silicon oxide, aluminum oxide, titanium oxide, tantalum oxide, and zinc oxide exists in an amorphous state at a grain boundary of crystal grain of an oxide of at least one kind selected from cobalt oxide, iron oxide, and nickel oxide. The media has a magnetic layer  13  made of an artificial lattice multilayer obtained by alternately laminating a Co layer or an alloy layer consisting of Co as a main phase and a metal element layer of at least one kind selected from Pt and Pd onto the layer  12.  Thus, a distribution of magnetic properties serving as a pinning site of the movement of a magnetic wall in case of recording information to the magnetic layer  13  is formed in the magnetic layer  13.

CROSS-REFERENCE TO RELATED APPLICATION

This application relates to U.S. patent application Ser. No. 09/604,633,filed Jun. 27, 2002, now U.S. Pat. No. 6,472,047 based on JapanesePatent Application No. 11-181434, filed on Jun. 28, 1999, the disclosureof which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to an information recording media for promptly andaccurately storing a large amount of information and, more particularly,to an information recording media for use as an information recordingdisk having high performance and high reliability and a magnetic storageapparatus and an magneto-optical storage apparatus using such a media.

DESCRIPTION OF THE RELATED ART

The progress of the recent advanced information society is remarkableand a multimedia in which information of various formats has beenintegrated is being rapidly spread. As an information recordingapparatus which supports it, there are a magnetic recording disk driveand a magneto-optical recording disk drive. At present, in the magneticrecording disk drive, miniaturization is being realized while improvinga recording density. In association with it, the realization of a lowprice of the disk drive is being rapidly progressed. To realize a highdensity of the magnetic recording disk, techniques (1) to shorten adistance between the magnetic recording disk and a magnetic head, (2) toincrease coercivity of a magnetic recording media, (3) to devise asignal processing method, and the like are indispensable techniques.Among them, in the magnetic recording media, an increase in coercivityis indispensable to realize a high density recording. In addition to it,to realize a recording density exceeding 20 Gb/in², a unit in which amagnetization reversal occurs has to be reduced. For this purpose, it isnecessary to microfine a size of magnetic crystal grain. As a method ofrealizing it, a method whereby a shield layer is provided under amagnetic layer has been proposed. As an example of such a method, U.S.Pat. No. 4,652,499 can be mentioned.

In a magneto-optical recording disk drive for writing, reading, orerasing by using a laser beam, it is effective to form a micro magneticdomain by using a laser beam of a short wavelength. In this case, sincea Kerr effect shown by an amorphous alloy of a rare earth element and aniron group element as a recording media decreases in association with adecrease in wavelength of the laser beam, a read output to noise ratio(S/N) decreases and there is a case where a stable information recordingcannot be performed. To solve such a problem, an artificial latticelayer obtained by alternately laminating Pt and Co showing a large Kerreffect even in a short wavelength region of 400 nm or less has beenproposed. As an example of such a layer, JP-A-1-251356 can be mentioned.

SUMMARY OF THE INVENTION

In the above related art, first, in the magnetic recording disks, thereis a limitation in a grain-size distribution control of crystal grain ofan information recording magnetic layer by a shield layer and there is acase where both micro grain and enlarged grain exist. In case ofreversing the magnetization and recording information, the micro grainis influenced by a leakage magnetic field from the peripheral magneticcrystal grain and the enlarged grain causes an interaction with theperipheral magnetic crystal grain to the contrary. Therefore, when anultra-high density magnetic recording exceeding 20 GB/inch² isperformed, there is a case where the stable recording cannot beperformed. This problem also similarly occurs in a magnetic recordingdisk having a magnetic layer for longitudinal magnetic recording and ina magnetic recording disk having a magnetic layer for perpendicularmagnetic recording of the Co—Cr system.

In the magneto-optical recording, if the artificial lattice layerobtained by alternately laminating Pt and Co is used as a recordinglayer, although a large Kerr rotational angle is obtained even in theshort wavelength region of 400 nm or less, a moving speed of a magneticwall is high. Particularly, in case of performing a mark lengthrecording, it becomes a cause of a jitter and the stable writing orread-back cannot be performed.

In consideration of the problems of such a related art, it is an objectof the invention to provide an information recording media suitable forperforming an ultra-high density magnetic recording, namely, a magneticrecording media or magneto-optical recording media. Another object ofthe invention is to provide a magnetic storage apparatus and amagneto-optical storage apparatus which are suitable for an ultra-highdensity magnetic recording.

The above objects are accomplished by controlling a distribution of amagnetization reversal size of a magnetic layer in an informationrecording media. The above objects are also accomplished by providing aportion serving as a pinning site of the movement of a magnetic wall fora magnetic layer in an information recording media.

That is, an information recording media according to the invention ischaracterized in that: it includes a substrate, an inorganic compoundlayer formed on the substrate, and a magnetic layer formed on theinorganic compound layer; the inorganic compound layer is a layer inwhich an oxide of at least one kind selected from silicon oxide,aluminum oxide, titanium oxide, tantalum oxide, and zinc oxide exists inan amorphous state at a grain boundary of crystal grain of an oxide ofat least one kind selected from cobalt oxide, iron oxide, and nickeloxide; and the magnetic layer is an artificial lattice multilayerobtained by alternately laminating a Co layer or an alloy layerconsisting of Co as a main phase and a metal element layer of at leastone kind selected from Pt and Pd. As an alloy consisting of Co as a mainphase, for example, Co—Cr, Co—Cr—Pt, or Co—Cr—Ta can be used.

The inorganic compound layer has a honeycomb structure in whichhexagonal crystal grains are two-dimensionally and regularly arrangedwhen it is seen from the direction that is perpendicular to a layersurface. It is preferable that the crystal grain in the inorganiccompound layer has a grain-size distribution in which a standarddeviation of the grain-size distribution of the crystal grain when it isseen in the in-plane direction is equal to or less than 10% of anaverage grain size. It is also desirable that a thickness of inorganiccompound layer lies within a range from 10 nm or more to 100 nm or less.A lower limit of the layer thickness is equal to a thickness at whichthe inorganic compound layer can be stably formed and an upper limit isdetermined by an internal stress which the inorganic compound layer has.

The magnetic layer has the same crystal shape as that of the crystalgrain in the inorganic compound layer and is formed by epitaxiallygrowing crystal grain of the magnetic layer in a column shape onto acrystal phase of the inorganic compound layer. Thus, the crystal grainof the magnetic layer exists in correspondence to the crystal grain inthe inorganic compound layer and amorphous or polycrystalline magneticcrystal grain exists in correspondence to a grain boundary phase of theinorganic compound layer. To form the magnetic layer of the artificiallattice multilayer structure onto the inorganic compound layer, it ispreferable to use a structure in which a Co layer is used as a firstlayer, the Co layer of the first layer is epitaxially grown from thecrystal grain of the inorganic compound layer, and Co which is formed inthe grain boundary phase is polycrystalline or amorphous.

A change in magnetic properties occurs in the magnetic layer in thelayer surface direction due to a difference of the crystallinestructure. That is, as for the magnetic layer, the magnetic propertiesof at least one of the magnetic anisotropy, coercivity, and saturationmagnetization differs in dependence on the portion which was epitaxiallygrown on the crystal phase of the inorganic compound layer and theportion grown on the grain boundary phase. Thus, the moving speed of themagnetic wall can be controlled by setting a pinning site of themagnetic wall movement in the amorphous or polycrystalline region. Byreflecting the structure of the inorganic compound layer of the lowerlayer and providing a portion of a different crystalline structure intothe magnetic layer as mentioned above, a distribution of the magneticproperties can be formed in the magnetic layer. If the distribution ofthe magnetic properties was formed in the magnetic layer, since themoving speed of the magnetic wall in the magnetic domain which is formedin the magnetic layer can be controlled in case of recordinginformation, the size of formed magnetic domain or the precision of theposition can be improved.

The information recording media according to the invention can be usedas a magnetic recording media for the magnetic storage apparatus or amagneto-optical recording media for the magneto-optical storageapparatus. The substrate can be made of an organic compound, aninorganic compound, or a metal. A glass substrate is suitable as asubstrate made of an inorganic compound. A substrate made of Al or an Alalloy can be used as a substrate made of a metal. An NiP layer can bealso formed on the substrate made of an inorganic compound or metal. Ahigh molecular material such as polycarbonate, polymethyl methacrylate(PMMA), amorphous polyolefin (APO), epoxy resin, or the like can be usedas a substrate made of an organic compound.

According to the invention, there is provided a magnetic storageapparatus comprising: a magnetic recording media; a magnetic recordingmedium driver for driving the magnetic recording media; a magnetic headfor performing a writing and a read to/from the magnetic recordingmedia; a magnetic head access system for accessing the magnetic head;and a read/write signal processing system for processing a write signaland a read signal of the magnetic head, wherein the foregoinginformation recording media is used as a magnetic recording media.

According to the invention, there is provided a magneto-optical storageapparatus comprising: a magneto-optical recording media; amagneto-optical recording medium driver for driving the magneto-opticalrecording media; an optical head for performing a writing and a readto/from the magneto-optical recording media; an optical head accesssystem for accessing the optical head; a signal processing system forprocessing a write signal and a read signal of the optical head; andmagnetic field applying means for applying a magnetic field to a regionon the magneto-optical recording media at a place near the optical head,wherein the foregoing information recording media is used as amagneto-optical recording media.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional schematic diagram of a magnetic recordingdisk;

FIG. 2 is a schematic diagram showing a TEM observation result of thesurface of an inorganic compound layer;

FIG. 3 is a schematic diagram showing a cross section of the inorganiccompound layer;

FIG. 4 is a diagram showing an X-ray diffraction profile of theinorganic compound layer;

FIG. 5A is a schematic plan view of a magnetic recording disk drive;

FIG. 5B is a cross sectional view taken along the arrows VB—VB in FIG.5A;

FIG. 6 is a cross sectional schematic diagram of a magneto-opticalrecording disk; and

FIG. 7 is a schematic diagram of a magneto-optical recording disk drive.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the invention will now be described hereinbelow withreference to the drawings.

[Embodiment 1]

An information recording media for magnetic recording (hereinafter,referred to as a magnetic recording disk) was manufactured. A magneticrecording disk drive in which the magnetic recording disk has beenassembled was manufactured.

FIG. 1 is a cross sectional schematic diagram of the manufacturedmagnetic recording disk. The magnetic recording disk has a laminatedstructure obtained by sequentially forming an inorganic compound layer12, a magnetic layer 13, and a protective layer 14 onto a substrate 11.A glass substrate having a diameter of 2.5 inches is used as a substrate11 for the magnetic recording disk. An object obtained by mixing CoO andSiO₂ at a mol ratio of 2:1 is used as a target, pure Ar is used as adischarge gas, and the inorganic compound layer 12 is formed on thesubstrate 11 by a sputtering method. A thickness of the formed inorganiccompound layer 12 is equal to 30 nm. An Ar pressure upon sputtering isequal to 3 mTorr and an input RF electric power is equal to 1 kW/150mmφ.

FIG. 2 is a schematic diagram showing a result obtained by observing thesurface of the obtained inorganic compound layer 12 by a transmissionelectron microscope (TEM). As shown in the diagram, the inorganiccompound layer 12 has a honeycomb structure in which almost regularhexagonal crystal grain 21 is two-dimensionally and regularly arranged.A target obtained by mixing CoO powder and SiO₂ powder at a mol ratio of2:1 and sintering a resultant mixture is used here. However, a layer ofa similar structure is also derived by a dual simultaneous sputteringmethod using a CoO target and an SiO₂ target.

FIG. 3 is a schematic diagram showing a result obtained by observing thecross section of the inorganic compound layer 12 by the TEM. As shown inFIG. 3, columnar tissues in the direction that is perpendicular to thesubstrate 11 are observed in the cross section of the inorganic compoundlayer 12. It has been found that the columnar tissue was grown withoutincreasing the crystal grain during the growth.

The crystal grain 21 and its grain boundary are analyzed by an EDXanalysis (μ-EDX analysis) of a micro region, so that the crystal grain21 is a Co oxide and SiO₂ exists at the grain boundary. The crystallinestructure of the inorganic compound layer 12 are analyzed by a θ-2θX-ray diffraction method, so that an X-ray diffraction profile shown inFIG. 4 is obtained. In FIG. 4, an axis of abscissa indicates an angle 2θand an axis of ordinate indicates a relative value of an X-raydiffraction intensity. As shown in the diagram, a diffraction peak of(220) of CoO is observed at a position near 2θ=62.5° and the other peaksare not observed. From an observation of a lattice image, it has beenfound that a cobalt oxide is crystalline and a silicon oxide isamorphous. A lattice constant obtained is almost equal to a value of Co.The lattice constant can be controlled in accordance with layer formingconditions and, further, by adding a metal (for example, chromium, iron,nickel, or the like) of a different ion radius into CoO or by addingoxides of those metals therein.

A grain-size distribution in the layer surface of the crystal grain 21is subsequently measured by the following procedure. A plane TEM imageobtained by the TEM observation is fetched as image information into acomputer and 250 pieces of crystal grains are selected at random fromthe crystal grain image observed in the same field of view. By imageprocessing with respect to each of the selected crystal grains by thecomputer, an outline of each crystal grain is extracted. An areaoccupied by each crystal grain is obtained by calculating an internalarea surrounded by the outline. Since the crystal grain observed by theTEM has almost a regular hexagonal shape, it is assumed that the shapeof the crystal grain is a regular hexagon. A length of side of thecrystal grain is calculated on the basis of the area of each crystalgrain obtained by the image processing operation, thereby obtaining acrystal grain size. With respect to the obtained crystal grain size, forexample, the number of crystal grains having a crystal grain size withina range from 5 nm or less than 6 nm, the number of crystal grains havinga crystal grain size within a range from 6 nm or less than to 7 nm, thenumber of crystal grains having a crystal grain size within a range from7 nm or less than to 8 nm, and the like are counted, respectively. Afrequency distribution of the crystal for the crystal grain size isobtained and this distribution is statistically processed, so that amean value of the crystal grain sizes and a standard deviation of thedistribution of the crystal grain sizes are obtained. The grain-sizedistribution of the crystal grain obtained in this manner has a normaldistribution. An average of the grain sizes (dimension between theopposite parallel sides) a of the crystal grain 21 is equal to 10 nm anda standard deviation a of the grain-size distribution is equal to 0.9nm. A distance b between the crystal grains is equal to 2 nm.

The number of crystal grains existing around one crystal grain issubsequently obtained by using the TEM image of the surface of theinorganic compound layer in accordance with the following procedure. Theplane TEM image obtained from the TEM image observation is fetched asimage information into the computer and image processed by the computer,thereby extracting the outline of the grain boundary portion of thecrystal grain. The 250 pieces of crystal grains are selected at randomfrom the outline image and the number of crystal grains existingadjacently, namely, the number of coordinations of the crystal grains iscounted with respect to each crystal grain. As for the obtained numberof coordinations, for example, the number of crystal grains having fivecoordinations, the number of crystal grains having six coordinations,the number of crystal grains having seven coordinations, and the likeare counted, thereby obtaining a frequency distribution of the crystalfor the number of coordinates. The average number of coordinates isobtained by statistically processing such a distribution. The 250 piecesof crystal grains are examined, so that the average number ofcoordinates is equal to 6.03. Also from the above results, it is backedup that the crystal grains having hexagonal shapes of similar grainsizes are two-dimensionally and regularly arranged to thereby form ahoneycomb structure.

An ultra structure multilayer (artificial lattice layer) is formed as amagnetic layer 13 onto the inorganic compound layer 12 by alternatelylaminating a Co layer and a Pt layer. The alternate lamination of the Colayer and Pt layer is performed by a dual simultaneous sputteringmethod. In this instance, a time difference is provided and a shutter ofa sputtering apparatus is opened so that the first layer becomes the Colayer. An input DC electric power is equal to 1 kW/150 mmφ.

A structure of the formed magnetic layer 13 is observed by the crosssectional TEM. Thus, as for the thickness of magnetic layer, a thicknessof Co layer is equal to 0.6 nm and a thickness of Pt layer is equal to1.8 nm. A thickness of the whole magnetic layer is equal to 50 nm. Asfor the thickness of Co layer and the thickness of Pt layer (or Pdlayer), it is desirable that a ratio of the thicknesses of both of themis set to Pt (Pd):Co=2:1 to 5:1 and the thickness of Co layer is equalto or less than 1 nm. When the thicknesses of the Co layer and Pt layer(or Pd layer) lie within such a range, a perpendicular magnetizationlayer having excellent magnetic properties can be obtained. The magneticlayer 13 and inorganic compound layer 12 are observed from acrystallographic viewpoint, so that although the Co layer formed on thecrystal phase of the inorganic compound layer 12 was epitaxially grown,the Co layer formed on the crystal grain boundary is a bulk substance ofmicro crystal or a polycrystalline substance. Although a DC sputteringhas been used here to form the magnetic layer 13, an RF sputtering orion beam sputtering can be also used. The magnetic properties and layerstructure of the magnetic layer 13 are not influenced by the sputteringsystem.

After the magnetic recording disk was magnetized in a constantdirection, the surface is observed by a polarization microscope. Thus,it has been found that although the portion corresponding to the regionon the crystal phase of the inorganic compound layer 12 becomes a goodperpendicular magnetization layer, the portion corresponding to theregion on the grain boundary is not the perpendicular magnetizationlayer. This result will be understood because in the region magnetizedin the perpendicular direction, when a polarizing plate is rotated, areversal of light and dark occurs. The portion corresponding to theregion on the grain boundary of the inorganic compound layer 12 is heldto be gray and the brightness does not change. The magnetic propertiesof the magnetic layer 13 are measured, so that the magnetic propertiesin which a coercivity is equal to 3.0 kOe and a perpendicular magneticanisotropy energy is equal to 5×10⁷ erg/ml are obtained.

Finally, a carbon layer having a thickness of 5 nm is formed as aprotective layer 14. As conditions for sputtering, an input DC powerdensity is equal to 0.5 kW/150 mmφ and a discharge gas pressure is equalto 5 mTorr. Although Ar is used here as a sputtering gas, a gascontaining nitrogen or a gas containing nitrogen and hydrogen can bealso used. Since the grain is microfined if the gas containing nitrogenor the gas containing nitrogen and hydrogen is used, a resultant layerbecomes fine and protecting performance can be improved.

After a high polymer material having a straight chain structure whosemolecular weight is equal to or larger than 3000 was coated as alubricant onto the surface of the magnetic recording disk manufacturedas mentioned above, the disk is assembled into the magnetic recordingdisk drive schematically shown in FIGS. 5A and 5B and read/writecharacteristics of the magnetic recording disk are evaluated. As shownin FIG. 5A as a schematic plan view of the magnetic recording disk driveand FIG. 5B as a cross sectional view of such a drive taken along thearrows VB—VB in FIG. 5A, it is the drive of a well-known constructioncomprising: a magnetic recording disk 31 which is rotated by a magneticrecording disk medium driver 32; a magnetic head 33 which is held by amagnetic head access system 34 and performs a writing and a read-backto/from the magnetic recording disk 31; and a read/write signalprocessing system 35 for processing a write signal and a read signal ofthe magnetic head 33.

A ring type magnetic head having a soft magnetic layer of a highsaturation magnetic flux density of 2.1T is used for recording. Aspin-valve magnetoresistive head is used for read-back. A distancebetween the head surface and the magnetic layer 13 is equal to 20 nm. Asignal corresponding to 30 GB/inch² is recorded onto the magneticrecording disk by a zone bit recording system and an S/N ratio of thedisk is evaluated, so that a read output of 32 dB is obtained. An errorrate of the disk is measured, so that it is equal to or less than 1×10⁻⁵as a value at the timing when no signal process is performed. The diskis observed by a magnetic force microscope (MFM), so that a zigzagpattern existing on a magnetic wall around the magnetic domain is alsoremarkably smaller than that of the media of the related art.

The signal corresponding to 20 Gb/in² is recorded onto the magneticrecording disk by using the magnetic head. With respect to thisrecording pattern, the read operation is performed just after the end ofthe recording operation and after the disk was left for 2000 hours afterthe recording and read signal intensities obtained are compared. Theread signal intensity after the elapse of 2000 hours indicates an outputof 99% of that just after the recording, the write signal is hardlydeteriorated, and an attenuation of the write signal which is caused bya thermal fluctuation or a demagnetization due to the heat does notoccur.

For comparison, a magnetic recording disk having almost the samestructure as that of the above disk except that the inorganic compoundlayer 12 is not formed is manufactured under conditions similar to thosementioned above. The read/write characteristics of the magneticrecording disk for comparison are evaluated by a method similar to thatmentioned above, so that since the magnetic wall is easily moved, anedge position of the magnetic domain is not determined and a jitterincreases to a value that is four or more times as large as that of themagnetic recording disk of the embodiment. The shape of the magneticdomain is observed by the MFM, so that concave and convex portions existand noises increase by 3 dB or more.

Although the example in which the magnetic layer was formed on theinorganic compound layer has been mentioned here, it is also possible toform a substrate by using the inorganic compound and directly form amagnetic layer onto the substrate. Although cobalt oxide was used as amaterial of a crystal phase of the inorganic compound layer in theembodiment, a similar effect can be also obtained by using iron oxide ornickel oxide in place of cobalt oxide. Although silicon oxide was usedas a material existing at the crystal grain boundary, a similar effectcan be also obtained by using aluminum oxide, titanium oxide, tantalumoxide, or zinc oxide in place of silicon oxide. Further, although theexample of using the Co/Pt artificial lattice multilayer as a magneticlayer has been shown here, a similar effect can be also obtained byusing a Co/Pd artificial lattice multilayer. As a substrate on which theinorganic compound layer is formed, a similar effect can be alsoobtained by using a substrate made of a metal such as Al, Al alloy, orthe like or a substrate formed by coating NiP onto a substrate of glass,Al, or Al alloy by a plating method besides the glass substrate.

[Embodiment 2]

An information recording media for magneto-optical recording(hereinafter, referred to as a magneto-optical recording disk) ismanufactured. A magneto-optical recording disk drive in which such amagneto-optical recording disk has been assembled is formed.

FIG. 6 is a cross sectional schematic diagram of the manufacturedmagneto-optical recording disk. The magneto-optical recording disk has alaminated structure obtained by sequentially forming an inorganiccompound layer 42, a magnetic layer 43, a magneto-optical enhancementlayer 44, and a light reflecting layer 45 onto a substrate 41. Apolycarbonate substrate having a diameter of 130 mm in which a guidegroove is formed on the surface is used as a substrate 41. To remove themoisture contained in the substrate, the substrate 41 is subjected to abaking treatment in the vacuum for three hours prior to forming a layer.Subsequently, the inorganic compound layer 42 is formed on the substrate41 by a sputtering method. When the inorganic compound layer 42 isformed, an object obtained by mixing CoO and SiO₂ at a mol ratio of 2:1is used as a target and pure Ar is used as a discharge gas.

A pressure upon sputtering is equal to 3 mTorr, an input RF electricpower is equal to 1 kW/150 mmφ, and a thickness of the formed inorganiccompound layer 42 is equal to 65 nm.

The surface of the obtained inorganic compound layer 42 is observed bythe TEM, so that a honeycomb structure in which the crystal grains 21 ofalmost a regular hexagon are two-dimensionally and regularly arranged isobserved as shown in FIG. 2. The cross section of the obtained inorganiccompound layer 42 is observed by the TEM, so that columnar tissues inthe direction perpendicular to the substrate 41 are observed in thecross section of the inorganic compound layer 42 as shown in FIG. 3. Thecolumnar tissues are grown without increasing the dimensions during thegrowth.

The crystal grain 21 and its grain boundary is analyzed by the EDXanalysis (μ-EDX analysis) of a micro region, so that the crystal grain21 is a Co oxide and SiO₂ exists at the grain boundary. The crystallinestructure of the inorganic compound layer 42 is analyzed by an X-raydiffraction method, so that a diffraction peak of (220) of CoO isobserved at a position near 2θ=62.5° as shown in FIG. 4. From anobservation of a lattice image, it has been found that a cobalt oxide iscrystalline and a silicon oxide is amorphous. A lattice constantobtained is almost equal to a value of Co.

A grain-size distribution of the crystal grain 21 in the inorganiccompound layer 42 is subsequently measured by a method similar to thatin the embodiment 1. The grain-size distribution is a normaldistribution, an average of the grain sizes (dimension between theopposite parallel sides) a of the crystal grain 21 is equal to 10 nm,and a standard deviation a of the grain-size distribution is equal to0.9 nm. A distance b between the crystal grains is equal to 2 nm. Thenumber of crystal grains existing around one crystal grain is obtainedby using the TEM image of the surface of the inorganic compound layer bya method similar to that in the embodiment 1, so that an average of thenumbers of crystal grains is equal to 6.02. Also from the above resultindicating that the number of crystal grains existing around one crystalgrain is equal to 6.02, it is backed up that the crystal grains havinghexagonal shapes of similar grain sizes are two-dimensionally andregularly arranged to thereby form a honeycomb structure.

An ultra structure multilayer (artificial lattice layer) is subsequentlyformed as a magnetic layer 43 onto the inorganic compound layer 42 byalternately laminating a Co layer and a Pt layer. The alternatelamination of the Co layer and Pt layer is performed by the dualsimultaneous sputtering method. In this instance, a time difference isprovided and a shutter of a sputtering apparatus is opened so that thefirst layer becomes the Co layer. An input DC electric power is equal to1 kw/150 mmφ.

A structure of the formed magnetic layer 43 is observed by the crosssectional TEM. Thus, as for the thickness of magnetic layer, a thicknessof Co layer is equal to 0.6 nm and a thickness of Pt layer is equal to1.8 nm. A thickness of the whole magnetic layer is equal to 20 nm. Asfor the thickness of Co layer and the thickness of Pt layer (or Pdlayer), it is desirable that a ratio of the thicknesses of both of themis set to Pt (Pd):Co=2:1 to 5:1 and the thickness of Co layer is equalto or less than 1 nm. When the thicknesses of the Co layer and Pt layer(or Pd layer) lie within such a range, a perpendicular magnetizationlayer having excellent magnetic properties can be obtained. The magneticlayer 43 and inorganic compound layer 42 are observed from acrystallographic viewpoint, so that although the Co layer formed on thecrystal phase of the obtained inorganic compound layer 42 wasepitaxially grown, the Co layer formed on the crystal grain boundary isa bulk substance of micro crystal or a polycrystalline substance.Although a DC sputtering has been used here to form the magnetic layer43, an RF sputtering or ion beam sputtering can be also used. Themagnetic properties and layer structure of the magnetic layer 43 are notinfluenced by the sputtering system.

After the magneto-optical recording disk was magnetized in a constantdirection, the surface is observed by a polarization microscope. Thus,it has been found that although the portion corresponding to the regionon the crystal phase of the inorganic compound layer 42 becomes a goodperpendicular magnetization layer, the portion corresponding to theregion on the grain boundary is not the perpendicular magnetizationlayer. This result will be understood from the fact that in the regionmagnetized in the perpendicular direction, when a polarizing plate isrotated, a reversal of light and dark occurs. The portion correspondingto the region on the grain boundary of the inorganic compound layer 42is held to be gray and the brightness does not change.

A silicon nitride layer having a thickness of 15 nm is formed as amagneto-optical enhancement layer 44. The magneto-optical enhancementlayer 44 is formed by using Si as a target and using an Ar/N₂ mixturegas as a discharge gas. A pressure of the Ar/N₂ mixture gas uponsputtering is equal to 10 mTorr, an input RF power density is equal to500 W/150 mmφ, and a refractive index of this layer is equal to 2.1.Finally, an Al₉₅Ti₅ alloy layer having a thickness of 50 nm is formed asa light reflecting layer 45.

Magneto-optical properties of the magneto-optical recording disk aremeasured, so that a Kerr rotational angle is equal to 0.97°, acoercivity is equal to 3.0 kOe, a saturation magnetization is equal to350 emu/ml, and a perpendicular magnetic anisotropy energy is equal to5×10⁷ erg/ml. A Currie temperature is equal to 200° C. and acompensation temperature is equal to 120° C. The magneto-opticalrecording disk manufactured as mentioned above is assembled into amagneto-optical recording disk drive as schematically shown in FIG. 7and read/write characteristics of the magneto-optical recording disk areevaluated. The magneto-optical recording disk drive is a drive of awell-known construction comprising: a magneto-optical recording media51; a disk drive system 52 for driving the magneto-optical recordingmedia 51; an optical head 53 for,performing a writing and a read to/fromthe magneto-optical recording media; a servo mechanism system 54 forpositioning the optical head 53; a signal processing system 55 forprocessing a write signal and a read signal of the optical head;magnetic field applying device 56 for applying a magnetic field to aregion on the magneto-optical recording media at a place near theoptical head upon recording; and a laser driver 57 for driving a laserbeam source of the optical head 53.

Information modulated by a (1, 7) RLL system is recorded onto themagneto-optical recording disk by a mark length recording system. Awavelength of the used laser light source is equal to 400 nm, anumerical aperture NA of the lens is equal to 0.59, a shape of arecording pulse is a multipulse, a writing laser power is equal to 8 mW,and a reading laser power is equal to 1.5 mW. When the recording isperformed by a specification of 640 MB per disk, a magnetic domainhaving a diameter of 0.3 μm is formed. The information is read back byusing a laser beam of the same wavelength, so that excellent readcharacteristics in which an S/N ratio is equal to 35 dB are obtained.

When a read-back light is irradiated onto the inorganic compound layer42, since a refractive index increases and a multiple interferenceoccurs between the magnetic layer 43 and substrate 41 at this time, theKerr rotational angle increases and a read signal output consequentlyincreases. Therefore, when a read-back light is irradiated to a specificmark, signals from the marks before and after the specific mark suddenlydecrease, so that the deterioration of resolution upon read-back due tocrosstalks can be suppressed.

For the purpose of comparison, a magneto-optical recording disk havingalmost the same structure as that mentioned above except that theinorganic compound layer 42 is not formed is manufactured underconditions similar to those mentioned above. Read/write characteristicsof the magneto-optical recording disk for comparison are evaluated by amethod similar to that mentioned above. Since the magnetic wall iseasily moved, a jitter is increased by two or more times. The shape ofthe formed magnetic domain is observed by the MFM, so that irregularconcave and convex portions exist on the circular outline and a noiselevel is increased by 5 dB or more.

Although the example in which the inorganic compound layer to control acrystallographic orientation of the magnetic layer was formed on theglass substrate has been mentioned, it is also possible to form asubstrate by using this inorganic compound layer and directly form themagnetic layer onto this substrate. Although cobalt oxide was used as amaterial of a crystal phase of the inorganic compound layer in theembodiment, a similar effect can be also obtained by using iron oxide ornickel oxide in place of cobalt oxide. Although silicon oxide was usedas a material existing at the crystal grain boundary, a similar effectcan be also obtained by using aluminum oxide, titanium oxide, tantalumoxide, or zinc oxide in place of silicon oxide. Further, although theexample of using the Co/Pt artificial lattice multilayer as a magneticlayer has been shown here, a similar effect can be also obtained byusing a Co/Pd artificial lattice multilayer. As a substrate, a similareffect can be also obtained by using amorphous olefin, epoxy resin,polymethyl methacrylate, or the like in place of polycarbonate.

According to the invention, since the distribution of the magneticproperties is formed in the magnetic layer and the pinning site forobstructing the movement of the magnetic wall is formed, the jitter andthe disk noises are reduced, and the high density magnetic recording canbe accomplished.

What is claimed is:
 1. A magneto-optical storage apparatus comprising amagneto-optical recording media, a magneto-optical recording mediumdriver for driving said magneto-optical recording media, an optical headfor performing a writing and a read to/from said magneto-opticalrecording media, an optical head access system for accessing saidoptical head, a signal processing system for processing a write signaland a read signal of said optical head, and magnetic field applyingmeans for applying a magnetic field to a region on said magneto-opticalrecording media at a place near said optical head, wherein: saidmagneto-optical recording media has a substrate, an inorganic compoundlayer formed on said substrate, and a magnetic layer formed on saidinorganic compound layer; said inorganic compound layer, is constructedby a crystal grain of an oxide of at least one kind selected from thegroup consisting of cobalt oxide, iron oxide, and nickel oxide, an oxidewhich exists at a grain boundary of said crystal grain and is amorphousand made of at least one kind selected from the group consisting ofsilicon oxide, aluminum oxide, titanium oxide, tantalum oxide, and zincoxide; and said magnetic layer is an artificial lattice multilayerobtained by alternately laminating a Co layer or a layer made of analloy having Co as a main phase and a layer having a metal element of atleast one kind selected from the group consisting of Pr and Pd.